The present invention relates generally to antennas, and more particularly, to a low-cost, very small antenna terminal (VSAT) antenna system for user subscriber terminals which may be used to access low-earth orbiting (LEO) and other satellite communications systems.
Currently planned Ka-band low-earth orbiting (LEO) satellite communications systems include Teledesic (Teledesic LLC) and Spaceways (Hughes) satellite communications systems. Typically, these satellite communications systems operate in the 20-30 GHz bandwidth region. The satellites carrying the communications systems orbit the Earth in low earth orbit at approximately 1400 kilometers. The satellites of a typical LEO constellation orbit the Earth in a matter of hours.
The satellite communications systems communicate with user subscriber terminals that each employ a very small antenna terminal (VSAT) antenna system. The user subscriber terminals are fixed on the Earth and sequentially acquire each of the orbiting satellites as they pass through the field of view of the antenna system. The antenna system thus forms a critical part of the LEO subscriber terminal that is used to communicate with the LEO satellite communications system. Because the LEO satellite communications systems are used to interface to a large number of subscribers, a low-cost antenna system is important to ensure purchase of systems by subscribers. A production cost target of $400-$500 is desired for a complete antenna system.
From a technical standpoint, the antenna system should provide high gain with a low noise temperature. The antenna system should operate with selectable circular polarization and low axial ratio. High isolation should be provided between 20 GHz receive signals and 30 GHz uplink signals.
Two independent beams are thus required, one that tracks an active satellite while transmitting and receiving, and another that anticipates the angular position of and has its receiver functioning for the rising of the next satellite that is to be communicated with. Upon hand-off to the rising satellite, the transmitter is switched to the new satellite and the cycle is repeated. Tracking may be done using stored or downlinked ephemeris data. The VSAT subscriber terminal may be accurately sited by an installing technician, such as by using the global positioning system and an electronic compass, for example.
Logistically, the antenna system should be robust in design and easy to produce in large quantities using proven methods. The antenna system should have excellent maintainability features. All components of the antenna system should be readily accessible, standardized and easily replaced. Also, the antenna system should function in severe outdoor environments.
It would therefore be desirable to have a low cost antenna system for use with user subscriber terminals used to communicate with low-earth orbiting satellites. Accordingly, it is an objective of the present invention to provide for a very small antenna terminal (VSAT) antenna system for use with user subscriber terminals and which may be used to communicate with low-earth orbiting and other satellites.